The methods of x-ray diffraction are being used to determine quantitative aspects of metalloporphyrin stereochemistry. Metalloporphyrins that are currently being studied include an iron (III) porphyrin with two axial thioether ligands. We also plan to continue our electronic structure - geometry correlations with the study of selected iron (II) porphyrin complexes. We plan to examine six-coordinate iron (III) porphyrins with nonequivalent axial ligands if appropriate synthetic procedures can be devised. We plan to continue our investigations of species utilizing imidazolate as a bridging ligand. Work currently in progress includes the study of a five-coordinate nitrosyl derivative of a manganese (II) porphyrin and a five-coordinate iron (III) porphyrin complex.